The exhaust gas generated during converter refinement contains carbon monoxide at a high concentration. As apparatuses that process this converter exhaust gas, there are a combustion type exhaust gas processing apparatus that recovers energy in a boiler after carbon monoxide in exhaust gas is combusted at the top of the converter and a non-combustion type exhaust gas processing apparatus that recovers carbon monoxide without combustion. As the non-combustion type exhaust gas processing apparatus, for example, an OG system converter exhaust gas recovery apparatus as described in Non-Patent Document 1 is typically used.
In refinement in a converter, first, the converter is charged with molten iron and decarburization refinement is mainly performed by converter blowing. After the completion of the refinement, molten steel is tapped, slag is removed, and molten iron is charged for the next refinement. In the converter refinement cycle as described above, a large amount of exhaust gas containing a high concentration of carbon monoxide is generated during the converter blowing. Exhaust gas is not generated while blowing is not conducted. Additionally, although the generation amount of the exhaust gas increases rapidly immediately after the start of blowing, a high concentration of oxygen is contained in the exhaust gas immediately after the start of the blowing, and the carbon monoxide concentration is not high. As time passes from the start of the blowing, the oxygen concentration in the exhaust gas drops, and the carbon monoxide concentration increases.
If the exhaust gas is started to recover when the carbon monoxide concentration in the exhaust gas is not high immediately after the start of the blowing, a quality of the recovered exhaust gas as fuel gas decreases. This is not preferable, and therefore, the exhaust gas is usually diffused into the atmosphere at the time of the start of the converter blowing as described in Patent Document 1. Also, a CO-in-gas concentration analyzer (furnace top CO analyzer) is provided on an exhaust gas path of a radiation section at the top of a converter to measure the carbon monoxide concentration in the exhaust gas, and if the carbon monoxide concentration in the exhaust gas rises to more than a given concentration, recovery of the exhaust gas to a gas holder is started.
As described above, the oxygen concentration in the exhaust gas is high immediately after the start of the blowing. Additionally, if damage or the like occurs in the exhaust path and ambient air is mixed into the exhaust gas, the oxygen concentration in the exhaust gas may increase. If the exhaust gas is recovered when the oxygen concentration in the exhaust gas is high, a component in the exhaust gas may exceed an explosion limit. Therefore, an oxygen-in-gas concentration analyzer (furnace top oxygen analyzer) is provided on the exhaust gas path of the radiation section at the top of the converter from a viewpoint of safety, an oxygen-in-gas concentration analyzer (furnace bottom oxygen analyzer) is provided at a flue after wet dust collection, and the exhaust gas is recovered to the gas holder only in a case where both the oxygen concentrations in the exhaust gas at these two places are a given concentration or lower.
At the time of the start of blowing, the exhaust gas from the flue is discharged to a flare stack by the operation of a three-way valve after a recovery valve is closed. After the start of the blowing, when the conditions that the carbon monoxide concentration measured by the furnace top CO analyzer becomes a given concentration or higher, for example, 25% or higher and the oxygen concentrations in the exhaust gas at two places measured by the furnace top oxygen analyzer and the furnace bottom oxygen analyzer become a given concentration or lower, for example, 2% or lower are established, for the first time, the recovery valve is opened, and the exhaust gas path is switched by the operation of the three-way valve to start the recovery of the exhaust gas to the gas holder.
In the oxygen concentration analysis in the converter exhaust gas, a method of sampling and analyzing gas within the flue (exhaust gas path) is generally used. For example, a paramagnetic oxygen analyzer using a wet sampler is used. Gas is sampled from the flue using a water stream, the sampled gas is introduced into the paramagnetic oxygen analyzer via a drain separator, a gas cooler, and a drain separator, and the oxygen concentration in the sampled gas is measured.
In converter gas recovery apparatuses of the related art, response delay of analysis in the furnace bottom oxygen analyzer is present. Therefore, there is a problem in that the timing at which recovery of the exhaust gas to the gas holder is started may be delayed after the start of converter blowing, and the converter exhaust gas that is combustible gas cannot be effectively utilized.
Additionally, as a gas analyzer, a laser type gas analyzer that irradiates measurement gas with laser light and measures the gas concentration from quantity-of-light changes caused by the light absorption of the laser light is disclosed in, for example, Patent Documents 2 and 3.
However, until now, there has been no example where the above laser type gas analyzer is applied to the converter gas recovery apparatus.